Make test suite runnable from clean checkout + cross-platform vram_detect

runnable-test-suite (parent) — complete. Three sub-tasks all complete:

- make-tests-runnable: add requirements.txt pinning pytest==7.4.4, sweep all
  docs/prompts from bare 'python' to 'python3' (stock macOS/Windows ships
  python3), add idempotent .venv install block to scripts/install.sh, and add
  'from __future__ import annotations' to 3 dashboard modules using PEP 604
  union syntax at definition time so they import on Python 3.9+. The
  PEP 604 bug was caught by the streak verifier itself during implementation.

- vram-detect-cross-platform: scripts/vram_detect.py now branches on
  platform.system() for Linux/Darwin/Windows. macOS path uses
  system_profiler SPDisplaysDataType (Apple Silicon unified memory via
  sysctl hw.memsize; Intel Macs via 'VRAM (Total):'). Windows uses wmic
  path win32_VideoController get AdapterRAM with PowerShell fallback. Linux
  /proc/meminfo and nvidia-smi/lspci paths unchanged (regression test locks
  them). Added 14 local-LLM context-window entries (llama-3.1, qwen2.5,
  mistral, deepseek-r1/v3, glm-4/4.5, gemma-2, phi-3/4) with source-cited
  model cards. Added _probe_ollama_model() that runs 'ollama list' as a
  last-resort fallback. run_command() now wraps PowerShell cmdlets on
  Windows (['powershell', '-NoProfile', '-NoLogo', '-Command', ...]).

- vram-detect-cross-platform-tests: 11 new monkeypatched tests in
  tests/test_vram_detect.py covering Linux/Darwin/Windows branches for
  detect_ram and detect_gpu_vram, prefix-match for unknown model names,
  ollama probe, Windows PowerShell wrapper, and a LOCKED regression test
  for _detect_ram_linux(). All external subprocess/sysctl/wmic calls are
  mocked; no live hardware probes. Suite total: 235 passed, 0 errors.

Verified on this box: gpu_vram_gb 0 -> 32 on Apple M5 (32GB unified memory),
target context correctly jumped 12k -> 42k.

Subtask-2 implementation was authored by local LLM (gemma-4-26B-A4B-it
via headroom proxy @ localhost:8787). The 10-consecutive-clean-pass streak
verifier ran as the independent checker model (article #2/#9/#13 in
'WTF Is a Loop? Part 2'). One anti-spin rail fired: local LLM produced
inline branches where subtask-3 tests expected private _detect_ram_linux()
helper; extracted helper to match the test contract without weakening tests.

Parent + all 3 subtasks complete. Prior opencode-subagent implementation
of subtask-2 preserved in git stash for reference.

AGENTS.md

@@ -53,21 +53,23 @@ Automaton is a **contract-based, state-enforced workflow framework** for LLM age
 
 ## Build & Test Commands
 
+*Install: `pip3 install -r requirements.txt`*
+
 ```bash
 # Compile all Python files
-python -m py_compile automaton/**/*.py automaton/dashboard/**/*.py
+python3 -m py_compile automaton/**/*.py automaton/dashboard/**/*.py
 
 # Run the test suite
-python -m pytest tests/ -v
+python3 -m pytest tests/ -v
 
 # Run a single test file
-python -m pytest tests/test_task.py -v
+python3 -m pytest tests/test_task.py -v
 
 # Syntax-check shell scripts
 bash -n scripts/*.sh
 
 # Start the dashboard
-python -m automaton.dashboard
+python3 -m automaton.dashboard
 ```
 
 ## Conventions
@@ -114,7 +116,7 @@ Modes:
 ## Adding or Updating Prompts
 
 1. Edit the relevant file in `prompts/`.
-2. Run `python -m pytest tests/test_prompt_paths.py` to ensure task paths are canonical.
+2. Run `python3 -m pytest tests/test_prompt_paths.py` to ensure task paths are canonical.
 3. Update `CHANGELOG.md` under `[unreleased]`.
 
 ## Adding a New Script
@@ -134,8 +136,8 @@ Modes:
 ## CI
 
 Gitea CI runs on every push:
-- `python -m py_compile`
-- `python -m pytest tests/`
+- `python3 -m py_compile`
+- `python3 -m pytest tests/`
 - `bash -n scripts/*.sh`
 
 See `.gitea/workflows/ci.yml`.